Atrial fibrillation is a common cardiac condition in which irregular heart beats cause a decrease in the efficiency of the heart, sometimes due to variances in the electrical conduction system of the heart. In some circumstances, atrial fibrillation poses no immediate threat to the health of the individual suffering from the condition, but may, over time, result in conditions adverse to the health of the patient, including heart failure and stroke. In the case of many individuals suffering from atrial fibrillation, symptoms affecting the patient's quality of life may occur immediately with the onset of the condition, including lack of energy, fainting, and heart palpitations.
In some circumstances, atrial fibrillation may be treated with drugs or through the application of defibrillation shocks. In cases of persistent atrial fibrillation, however, surgery may be required. The surgical procedure originally developed to treat atrial fibrillation is known as a “MAZE” procedure where the atria are surgically cut apart along specific lines and sutured back together. While possibly effective, the MAZE procedure tends to be complex and may require highly invasive access to the thorax. In order to reduce the need to open the atria, thermal ablation tools have been developed to produce lines of inactive tissue along the heart wall that mimic the MAZE procedure. This is most commonly done using radio frequency (RF) ablation devices to ablate and electrically isolate tissue that may be responsible for the improper or electrical conduction that causes atrial fibrillation.
A variety of cardiac ablation devices and methods are currently available for treatment of atrial fibrillation and other arrhythmias. With some systems, endocardial tissue is contacted and ablated, for example via a catheter-based ablation instrument. Conversely, epicardial tissue can be ablated. Conventionally, cardiac surgeons access the epicardial tissue via a standard sternotomy. More recently, certain atrial fibrillation treatment procedures have been advanced that entail ablating small segments of epicardial tissue on a minimally invasive basis, such as via a single or bilateral thoractomy approach. For example, the junctions of pulmonary veins with the left atrium have been identified as being a common area where atrial fibrillation-triggering foci reside. For many patients, then, atrial fibrillation can be effectively treated by ablating only a portion of the complete MAZE pattern, such as at the pulmonary vein/left atrium junction. More particularly, a viable cardiac arrhythmia treatment technique entails ablating an epicardial lesion into the posterior left atrium around or circumscribing the left pulmonary veins and another epicardial lesion encircling the right pulmonary veins. These island ablation lesions can be formed on a minimally invasive basis via bilateral thoractomy using clamp-type ablation instruments, for example a surgical ablation device available under the trade name Cardioblate® Gemini™ available from Medtronic, Inc. While well-accepted, the bilateral thoractomy surgical approach may require the surgeon to perform various additional procedures, such as dissection of pericardial reflections, in order to laterally access the posterior left atrium ablation site(s). Additionally, while the pulmonary vein island ablation represents only a small portion of a complete MAZE procedure, additional epicardial lesions along the left atrium may be beneficial to prevent re-entry of an unwanted sympathetic pathway.
In light of the above, a need exists for systems and methods of making epicardial lesions on selected cardiac locations on a minimally invasive basis, such as along the posterior left atrium via a subxiphoid surgical approach.